1. Field of the Invention
The present invention concerns a coupling link for welded chain and more specifically concerns a coupling link for welded link chain made up of two parallel spaced legs, two curved end parts joining the legs together to give the loop structure and a stud placed between the legs within the loop. The coupling link is made in two link halves that may be separated and then fixed together using a locking rod running through the two legs and the stud. The two link halves are such that each part has a short leg with a pin, a curved end part, and a long leg having a hole therein for receiving the pin of the shorter leg of the other half. The link has inner faces thereon for fixing the stud in position therebetween.
2. Description of the Prior Art
Welded link chains are used as driving connections between pulleys round which they are guided, wherein the outer faces of the pulleys must have regular pockets therein to take up the links of the chain. The links which are flat against the outer face of the pulley are joined together by upright links whose plane is in, or parallel to, the plane of the pulley. The coupling link of the present invention is constructed so that it may be run in either of the two possible positions in relation to the outer face of the pulley, that is, resting flat in a pocket in the pulley or in the plane of the pulley. In this respect it is different from prior art emergency chain repair links while, however, being similar in that it may be taken off or put on at any time desired. The coupling link of the present invention is, furthermore, to be distinguished from other coupling links that are designed for running in only one plane on a pulley, this normally being a plane parallel to the plane of the pulley.
One example of the prior art, of which the present invention is a further development, is the coupling link disclosed in the British patent specification No. 1,043,478, wherein the cross-section of the pins were made as large as possible in view of the static shearing forces. For this reason the cross-section of the pins were made so large that they extended as far as the middle transverse plane of the coupling link because in the outer direction the pins may only go as far as the start of the rounded end parts of the link. In this construction, the various parallel load bearing faces of the link were out of line with each other at the end faces of the stud. By accommodating the load bearing function, the sides, facing the rounded ends of the link, had a partly straight and a partly curved saddle line, which can be seen in the plane of this flat coupling link.
Normally the stud and the two halves of such a coupling link are drop forged. The two faces which are separated by a step on the finished drop forging then have to be machined in a number of stages. To this end, the workpiece is forged to be oversized so that the excess material can be machined away by broaching or milling.
However, such a known coupling link has shortcomings in use and there are some problems in connection with machining the link surfaces. If the flat coupling link is not positioned on the driving pulley so as to be parallel to the plane of the pulley but is flat against the outer face of the pulley, the rounded parts of the chain links next to the coupling link are turned so far that the studs thereof are violently forced against the faces of the stud of the coupling link. The saddle line of the stud of the coupling link experiences a load or force acting on the stud in a direction transverse to the plane of the coupling link. This transverse load imposes a shearing load on the locking rod. For this reason the coupling link may be damaged or even forced open resulting in breakage of the chain.
The machining, i.e. broaching, of the load bearing faces in the manufacture of such a flat chain coupling link has the effect of cutting the fiber or grain of the metal that has been produced during the forging process so that the strength of such a flat chain coupling link is greatly decreased. Furthermore, after broaching, there will be sharp edges or burrs near the pins on the legs and on the end faces of the pins. When the chain is then used in a position where the coupling link is rested flat on the outer face of the pulley (and not placed upright thereon) these sharp edges will be stressed and cold-worked in different ways. This leads to the formation of hairline cracks that in turn could cause fatigue failure in such a coupling link, in other words, the fatigue life of the coupling link is significantly reduced due to the stress formations as a result of these changes in load direction that take place before fatigue failure.
These problems make the machining of such forged parts of the known form of flat chain coupling link relatively complex, because the different faces on the two legs of the link and the two end faces of the stud are not in an upright plane but out of line in parallel planes so that the broaching of the legs of the coupling link has to be accomplished with a needle-like broach. Round milling or broaching cutters cannot be used because of the small amount of clearance between the faces inside the coupling link. Furthermore, the machining of the studs, and more particularly of a number of studs put together in the form of a stack, is very hard to undertake because the projecting faces are out of line with each other in the sideways direction. For these reasons the edges of the load bearing faces may not be machined fully to obtain a higher fatigue resistance.
In the case of the prior art coupling links discussed above the experience has been that the force transmission capacity is not high enough, as demonstrated by the fact that the load bearing faces exhibit signs of deformation after the flat coupling link has been in use for some time. Furthermore, fatigue fractures are frequent. These fractures start at the outer end faces of the pins and run through as far as the rounded parts of the coupling link. To solve this problem, it has been suggested to reinforce the flat coupling link in this area, such as making the links of steel of the same composition as used for the normal welded links of the chain. The outcome of this suggestion was a flat chain coupling link in which the middle stud was rounded off to conform with the shape of the links joined by the coupling link and the stud and the pins were symmetrical about the middle plane of the coupling link formed by the two halves and the end faces of the short leg sections lined up with each other. The rounded parts of the coupling link then had to be reinforced so that the coupling link may only be run in an upright position on the pulley, that is, with its plane parallel to the plane of the pulley. An example of this prior art construction is disclosed in the German Offenlegungsschrift specification No. 2,813,748. A number of attempts have been made to solve these problems, for example, by turning the chain when using such a flat coupling link, or in other cases by using a number of such flat coupling links with round chain links. In general, it has turned out that these shortcomings of the known flat chain coupling piece are so serious that these couplings are not used at all in general applications and especially in mining applications.
Furthermore, the machining of the load bearing faces of the flat chain coupling, that is, those faces abutting against the stud, is certainly not made any simpler even with the symmetrical form, because the reinforced rounded end pieces result in an inner space much smaller in size which makes machining this space very difficult.
The coupling link of the present invention is made in two like halves so that it may be taken apart and put together again. For joining two lengths of chain each of the halves is threaded through the end links of the pieces of chain and then the halves are moved together in their own plane such that the pin of one half is slipped into the hole in the other half and vice versa. The stud is then placed into position between the two link halves. Generally, the prior art locking rod used for locking the two halves together has frequently been designed to take up shearing and tension forces. In the present invention, the locking rod used to lock the two halves together, after being placed in position, does not experience any shearing forces.
In the present invention the necessary tensile strength is provided by the legs and the stud as the bearing faces of these parts are placed and so locked together that the tension or pulling forces at the rounded end parts are taken up thereby. It is necessary for the link to be constructed with such a geometry that, on the one hand, the chain will be fully resistant to the high tension or pulling forces and changes in the loading forces as is necessary in the case of heavy duty mining equipment chain applications while, on the other hand, the chain coupling link must run smoothly over the drive pulleys.